If you take Air Asia they will charge you if your luggage is over 30 kg. Unfortuately I had to take that airline as I was going to Chieng Rai in the early evening and that was my only option from Suvanabhumi. They did not weigh my carry on luggage. This was just one month ago. This is the cheapest airline. Didn't care about cheap but it was convienent. Will take Thai Air when I can.

Have a good trip